1. Field of the Invention
The present invention relates to an optical lens assembly for moving lenses for use in a photographic camera or a television camera and, more particularly, to a zoom lens apparatus with a motor for driving the zoom lens being incorporated therein.
2. Description of the Prior Art
In some conventional zoom lens apparatuses, there provide a zoom lens group composed of a variator lens and a compensator lens, and a zooming cam group having a cam groove, a transmission gear, a reduction gear and a clutch mechanism for separating the transmission between the transmission gear and the reduction gear to smoothly perform the operation, both the zoom lens group and zooming cam group being controlled by a motor through a reduction gear thereby to vary zoom ratios.
However, such a conventional zoom lens apparatus is generally referred to as a system wherein a motor for driving the lens drives the reduction gear by the rotating force of a rotary member located at the center of the rotation normally called a power rotor, and is controlled by the fed current.
Thus, when the power motor is built in within the zoom lens apparatus, the power motor, the reduction gear are so arranged around a lens barrel, which is out of the light path of the lens that the zoom lens apparatus becomes larger in its outer diameter, becomes non-cylindrical into an elliptical shape, and becomes hard to be handled. Also, as a transmission gear and a clutch are required for the reduction gear and the zooming cam group, the construction of the zoom lens apparatus becomes complicated, thus resulting in higher cost. To vary the zooming speed, the voltage to be applied upon the ends of the power motor, or resistors connected in serial are varied to control the current fed to the power motor thereby to limit the zooming speed. Accordingly, the rotating force of the motor is reduced in proportion to the current so that the rotation of the motor becomes weak enough to sometime come to a stop in the location of that the zooming speed is slow, resulting in that the zooming speed cannot be controlled.
Also, the zoom ratio is varied by the on and off of the power-supply switch for feeding the current to the power motor, so that the zoom ratio cannot be set in advance. Therefore, it is necessary to do that the image is confirmed and judged by an optical or electric view finder to stop the zooming. Accordingly, it is not known that the zoom ratio has been stopped from what ratio to what ratio.
In addition, in a case where the camera body is secured by a tripod or the like and the zooming operation is performed by a remote controller, which allows the user to control the photographing and zooming from a remote place, the images cannot be confirmed and, thus, the condition of the images is not known, where the zoom ratio has been moved from what ratio to what ratio or how many the zoom ratio is now.